Steel cords constituted by steel wires intertwined together are used as reinforcing members in tires, conveyor belts, rubber hoses, and other rubber products. A steel cord is known that has a stranded structure of a plurality of sheath strands intertwined around the outer circumferential surface of a core strand (for example, see Japanese Unexamined Patent Application Publication No. 2012-036539A). To manufacture these rubber products, a reinforcing layer formed of an arranged plurality of steel cords is embedded in an unvulcanized rubber member to form a molded article. Thereafter, the molded article is heated at a predetermined temperature and pressurized at a predetermined pressure in a vulcanization process to vulcanize the unvulcanized rubber. Thus, a rubber product embedded with a steel cord reinforcing layer is completed.
When the rubber product is in use, tensile forces and compressive forces act upon the embedded steel cords. The present inventors found that in a rubber product that includes a steel cord with a stranded structure of a plurality of sheath strands intertwined around the outer circumferential surface of a core strand, the wires (steel wires) that constitute the steel cord rub against one another when the rubber product is in use, this rubbing impacting upon hysteresis loss.
For example, in the case of a conveyor belt rubber product, operating with high hysteresis loss results in a problematic increase in the power needed to operate the conveyor belt. Based on their findings, the present inventors performed research and arrived at the present technology, which is capable of reducing hysteresis loss attributable to a steel cord embedded in a rubber product when the rubber product is in use.